1. Field of Invention
The present disclosure relates to downhole pumping systems submersible in well bore fluids. More specifically, the present disclosure concerns actively controlling flow to the intake of a submersible pump. Yet more specifically, the present disclosure relates to a method and apparatus for actively restricting gas flow and/or flow from a higher zone to an electrical submersible pump.
2. Description of Prior Art
Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the well bore to the surface. These fluids are generally liquids and include produced liquid hydrocarbon as well as water. One type of system used in this application employs a electrical submersible pump (ESP). ESPs are typically disposed at the end of a length of production tubing and have an electrically powered motor. Often, electrical power may be supplied to the pump motor via wireline. Typically, the pumping unit is disposed within the well bore just above where perforations are made into a hydrocarbon producing zone. This placement thereby allows the produced fluids to flow past the outer surface of the pumping motor and provide a cooling effect.
With reference now to FIG. 1, an example of a submersible ESP disposed in a well bore is provided in a partial cross sectional view. In this embodiment, a downhole pumping system 12 is shown within a cased well bore 10 suspended within the well bore 10 on production tubing 34. The downhole pumping system 12 comprises a pump section 14, a seal section 18, and a motor 24. The seal section 18 forms an upper portion of the motor 24 and is used for equalizing lubricant pressure in the motor 24 with the wellbore hydrostatic pressure. Energizing the motor 24 then drives a shaft (not shown) coupled between the motor 24 and the pump section 14. Impellers are coaxially disposed on the shaft and rotate with the shaft within respective diffusers formed into the pump body 16. As is known, the centrifugal action of the impellers produces a localized reduction in pressure in the diffuser thereby inducing fluid flow into the diffuser. In this embodiment, a series of inlets 30 are provided on the pump housing wherein formation fluid can be drawn into the inlets and into the pump section 14. The source of the formation fluid, which is shown by the arrows, are perforations 26 formed through the casing 10 of the well bore and into a surrounding hydrocarbon producing formation 28. Thus the fluid flows from the formation 28, past the motor 24 on its way to the inlets 30. The flowing fluid contacts the housing of the motor 24 and draws heat from the motor 24.
In some situations submersible pumping systems are disposed in a section of a wellbore between two producing formations or zones. For example in a dewatering situation the upper zone primarily produces gas whereas the low zone produces water. Thus with reference now to FIG. 1, the upper formation 29 is shown producing a mixture of water and gas flowing through the perforations 27. The upwardly directed arrow AG represents gas flowing up the borehole 8 and the downwardly directed arrow Aw represents water (or other liquids) flowing down the borehole 8. In some situations the upper formation can cause problems for the pumping system 12. For example, too much water flow from the upper formation 29 can restrict water production from the lower formation 28 thereby limiting liquid flow across the pump motor 24 and its corresponding cooling effect. Additionally, excessive gas from the upper formation can become entrained with the downflowing water and potentially cause pump cavitation. Gas from the lower formation can also make its way to the pump inlet.